On Fri, Jul 31, 2015 at 3:32 PM, Peter Maydell <peter.mayd...@linaro.org> wrote:
> On 31 July 2015 at 10:29, Naman patel <naman...@gmail.com> wrote: > > Can someone explain me what happens when a guest OS calls "invlpg" on say > > page swap out or a context switch? What exactly is the call flow and how > > QEMU handles this instruction? > > When we see the instruction during translation, we emit code > which will > In which function does the translation takes place? > * get the argument to invlpg (extracting it from the > relevant register, adding any constant offset required for > the addressing mode, etc) > Where exactly is it done? > * make a call to helper_inlvpg(). > (target-i386/translate.c has the C code that does this codegen -- > search for invlpg) > Thanks I got this function. > > Later when that generated code is run, we call the helper, which > does what it needs to do (in this case flush a page from QEMU's > TLB cache). When the call returns we'll carry on executing whatever > guest instruction comes next. > > > Also is there anyway QEMU can send some data > > back to the guest OS? > > > INVLPG is just an x86 instruction that performs an operation; > it doesn't modify any registers or flags. So there's no way > for it to tell the guest OS anything. > True that INVLPG only invalidates a TLB entry but in general how can one send a data structure(DS) back to guest OS from QEMU? I want to write my own function that can send a DS back to the guest OS. Are there any similar functions already present that sends back DS to guest? Or is it feasible? > > -- PMM > Thanks a lot for this information. It helped a lot. Regards, Naman
